Certain peculiarities of propeller-hull interaction

Abstract

Object and purpose of research. This paper analyses the peculiarities of propeller performance curves and propeller-hull interaction to find out their hydrodynamic reasons. Materials and methods. Propeller performance curves of modern naval ships, both open-water and behind the hull, intersect at low advance ratios, which results in negative wake fractions and growing wake non-uniformity effect upon torque ΔiQ. The reasons for these phenomena are analysed using the data on foil aerodynamics and attack angles of propeller blade elements. The study is performed as per analytical and theoretical approaches. Main results. The study shows that propeller blade elongation is usually equal to 2-4. Attack angles are the highest at blade roots that may have non-linear flow patterns as load grows; this effect is further increased by propeller operation in non-uniform hull wake. Blade skew is a secondary factor. Case studies of this paper illustrate the non-linearity of propeller performance curves in other cases. Conclusion. The main reason for these peculiarities of propeller hydrodynamics is non-linear lifting force coefficient of their blade root elements: at high loads, blade roots suffer flow separations due to non-linear lifting force.

Keywords

• propellers
• naval ships
• carrier vessels
• non-linear lifting force
• self-propulsion tests